MPG optimised header ideas
 

So, I've been thinking about building an MPG-optimised header for my civic CXi... (Why? To see if it works, of course :p) probably will be a while before I make a start on it even if I do decide to do it of course, given I have 1000 other things to and haven't even gotten around to installing my MPGuino yet :turtle: but I thought I'd throw a couple of ideas out there. Posting in Unicorn Corral as it's a potentially controversial suggestion and, of course, it may remain mythical due to time / money constraints.

Why it might work:

• I'm not talking about fat "high flow" headers off ebay or from a performance shop, this would be specifically designed and built to optimise low rpm torque (without sacrificing too much top-end of course - having the same peak power as stock would be fine by me).
• I've heard the VX has a specific header designed for efficiency, but looking at it, it's no great prize - short cast iron pipes straight into a cat, the only thing it seems to have going for it is small primary runner diameter. Oh, and a small amount of exhaust pulse overlap from the 1-2, 3-4 pairing *may* help the scavenging of cylinders 1 and 4, but it's dubious.
• "tri-y" or 4-2-1 headers can enhance low-end torque as well as high-end. Of course, people tend to measure at WOT, but if the torque is higher at WOT then presumably the original torque will be available at some value of partial throttle.
• We’re basically unrestricted with exhaust header design here, as long as you don’t eliminate the cat, oxygen sensors or other emissions equipment - and the cat on this car is the ‘under the body’ kind, not the sort that sits right on the exhaust ports, which makes longer tuned pipes a real possibility.

Background, based on a bunch of internet reading :D (feel free to jump in!):

Conventional wisdom is that short fat primaries are good for top-end rpm, while long thin ones are good for low rpm. However, it seems that within the 'butter zone' of primary diameter where you're neither choking the engine nor slowing the exhaust excessively, going a little smaller hurts the top end less than going larger hurts low-end torque.

There are two traditional designs, the 4-1 (all cylinders collect at one point) and the 4-2-1 (pairs of cylinders are connected using Y merge junctions, then the resulting two runners are connected using a third Y merge). The 4-1 can be tuned for a high and narrow peak power band but can sacrifice low-end torque even compared with a stock manifold, while the 4-2-1 apparently can give smaller gains across the board, including the low rpm range, at the expense of some peak power.

Equal length tubes, again, can be used to optimise for specific rpms, while slightly unequal lengths can spread out the resonances and produce a smoother torque curve.

At each Y merge in a 4-2-1, it’s recommended to step the size of the tube up slightly to cope with the combined flow - 15-30% in area seems to be recommended Y merges for ’street’ headers, though it’s more important with the last Y, as the first ones should have exhaust pulses coming in at 180 degree phase to each other (360 degrees of crank rotation). See http://coneeng.com/pdf/Area_Calculation_Table.pdf

Stainless steel is a better insulator than mild steel, and ceramic coating helps even more - this is important because apparently keeping the exhaust speed up is vital for scavenging especially at low rpm, and gas that cools gets smaller and therefore slows down.

A newish development appears to be a 'hybrid' / 'long tri-y' design, utilising primary runners similar in length to a traditional 4-1 design (generally much longer than the primaries in a 4-2-1) - or even longer, with a step in the primary diameter, and longish secondary runners. Putting a step from smaller diameter to larger apparently helps stop reversion (high pressure reflected exhaust pulses going the wrong way) as well as providing an extra reflection point in a longer runner. There are also ‘reversion preventers’ out there that have a step followed by a gentle taper back to the original size, but the jury is still out on them.

Another 'new' idea is a slight 'restriction' in diameter at junctions to produce a greater venturi effect in sucking out exhaust gasses from the other branch.

There is also a set of simple formulae I've found in various places on the webs which are 'guaranteed to spit out something useful' as a header design, which are implemented in this calculator here.

Design:

Using the above calculator, with values of
Exhaust Open BBDC. = 60
Exh close ATDC. = 20
CC of one "Cylinder" = 400

at 5800 rpm (roughly peak torque for a honda D16)
5800rpm (peak torque)
P = 32”
primary ID = 1.42”
P1 = 15”
P2 = 17”
secondary ID = 1.86”
CL = 5.6”
TP ID = 1.91”
TL = 29.8”

at 2400 rpm (5th gear at 100kph, a nice highway cruising speed)
P = 82”
primary ID = 0.91”
P1 = 15”
P2 = 67”
secondary ID = 1.198”
CL=3.6”
TP ID = 1.23”
TL = 81.8”

… and now for the hybrid ‘long-runner tri-y’ mashup. Note that the formula & calculator always use 15” for primary length, apparently “this is the best length” or something.

So, the trouble with primary diameter… the actual exhaust ports on the engine are oval 1.75” x 1.3125”, which is similar in area to a 1.5” ID tube - the above equations suggest anything over this is a waste of time and ideally smaller would be good, but we don’t want a ‘step’ in the wring direction, so 1.5” ID it is.

The primary length to the first set of Ys (our ‘P1’) is then the ‘P’ from the 5800 rpm calculation - 32”. Of course, many sources are quite insistent on the ’15 inch’ thing, and it would be nice to take advantage of anti-reversion effects, so we may as well put a step there, out to 1.625” ID, which is the next standard tube size.

At the first set of Ys, we don’t want too much increase in size (see above), so we only go up to the next standard size, 1.75” ID (area increase of 16%). This is about 10% less area than the formula spits out for 5800rpm, but hopefully should be OK.

Now, the total header length for the 2400rpm calculation is pretty darn long, with P=82” - I don’t like the idea of trying to put the last Y all the way back there, because I’d probably have to move the cat, which I’d rather not. So rather than that, I may as well use the cat as the last reflector for the 82” resonator, and bring the last Y forward a bit… so we can put the last Y at, say, 75” and run a 2” ID collector, with a restriction of around 1.875” (15% increase at the venturi, total step up of 31%). References say that you can almost ignore everything after the cat due to its damping effect on resonance, so I will ;)

Sanity checks:

Ebay headers for D16s appear to have primaries of about 1.75” - this probably makes fabrication easier (you don’t have to dolly the tubes out to match the ports, you can just weld round tube straight on), but it has to be hurting the low RPM power, based on the header formulas etc. (‘serious’ performance headers are larger, but intended for racing with heavily modified engines) … even 1.5” is more appropriate to 6500rpm according to the calculator, but given the port size I think it’s the smallest that can reasonably be fitted.

On the other end of the scale, some info on stock manifold primary tube sizes would be interesting for comparison - however, I strongly suspect that a nicely fabricated mandrel-bent ceramic-coated header with ballpark sensible tube sizes is going to flow nicer at any speed the low cost cast iron jobbie even if the length is a bit longer and the tuning isn’t exactly spot-on. Well, I hope, anyhow.

I’m pretty sure this will all fit, but getting that extra length before the cat will need some interesting design - I’m thinking a ‘ramhorn’ style manifold, in the style of the “k-tuned” headers might do it… luckily I quite enjoy TIG welding :D

Wrap up:

Crazy idea I know, and I have no idea if or when I’ll get time to try it, but it’s fun to play around with. What would be quite nice is to get access to some 1D exhaust simulation code to validate the above design, but the software seems to be on the “very expensive” side. On the other hand I think the design above looks pretty sensible (to my inexperienced eye), so the old “try and see” approach may just work.

I wouldn't Unicorn this; certainly it can work.

Sounds like you have already done a ton of homework on the matter and have probably thought it out more than the most header companies. In their defense, they plan to sell to a certain group of car owners who are typically runneing higher RPM than is necessary so the larger tubes are more than likely ideal for the market. Having a Honda you have the wonderful world of used parts at your disposal, I think the easiest way to try this is to buy a used 4-2-1 header and make new primaries. If you can't bend pipe, maybe just weld in smaller tube on the straights for a "quick" test mule piece. Either way I think it could be something worth looking into, many people with small block V8s have claimed increases in MPG after installing headers. Whether or not the Honda manifold chokes the engine as much as the old Chevys did is unknown but the principle is still there.

FWIW I've heard that some of the best custom made headers have Venturis because of their benefits. These are most likely performance benefits but just might help MPG too.

I'd go with variable geometry - for better everything. ;)

Couple of notes: is there room for the length you'll need under the car? Probably the prime reason OEM still makes cast headers. Some empirical data suggesting having the tube resonate at your desired rpm increased flow. Have you incorporated anti-reversion? I have also seen data suggesting flow was similar to a concept called "hull speed" in sailboats.

I say go for it, doesnt look unicorn to me.

You'll find that most of the headers you can find are designed the way they are to fit inside the engine bay or to work with the stock downpipe or something, not performance. Exhaust is hotter and under higher pressure than atmospheric, so generally you want rather long headers compared to stock for any reason.

I would just buy a budget header that the go-fast crowd has had good experiences with (they'll post dynos and stuff) and the worst that could happen is that you save a little weight and you gain a couple horsepower. Stock headers suck, period.

If you want to go "variable", one thing to try is a throttle plate inside the exhaust. Honda did it on a motorcycle before I believe, it adds restriction but gives them the ability to tune the harmonics a bit to prevent reversion.

Very interesting. Mazda skyactive engines have revised chassis tunnels to accomodate long headers. Its supposed to keep hot exhaust gas reversion from messing up the high compression. Yeah, why not do to the exhaust what they do upstream in the intake with valving. There seems to be some issues with the valving being robust enough on both ends with some diesel makes. Would an exhaust valve introduce too much drag in this example?

I skimmed over this, most looks pretty good. But I would not exceed exhaust valve size (in a 2 valve) for primary pipe size. That rule of thumb works exceedingly well for S/R (hot street, mild race) setups. If you are really looking to eco-mod with a custom header, smaller is better and 1.75" primaries are BIG. A better bet would be an after-header setup like the "acoustic supercharger" system, but it is not available for many cars.
My son and I built one (him mostly, high school shop class) I will see if I can scare up a pic. But remember, it is for a V6 or V8 setup as constructed.

Just a general reply to a few different posters:

The 'Unicorn Corral' part is also somewhat to do with the likelihood of this bubbling up to the top of my projects queue any time soon... :turtle: that may change of course...

Yes, I'm looking at 1.5" primaries, it's the smallest size that matches the port area.

Great idea about using half of an ebay 4-2-1, that just might work.

Planning on fitting it by using a "ramshorn" layout at the exhaust valve - have yet to measure though.

Variable geometry is fascinating, but I'm at the limits of finding good design info on long 4-2-1s as is... might keep this one 'simple' ;)

For fabrication - I love TIG welding, and mandrel bends aren't stupidly expensive (see ECS engines for example). Also there's a local shop that does CNC mandrel bending for reasonable prices. Will see how I go.

Should be the best case :thumbup:
We always strived to avoid a "Reverse Step" or neck down with a step in exhaust ports.



Don't think I had any input here, but splitting a 4-2-1 into two 2-1 headers and then running them into an X-Pipe would achieve the ASC design.

Here are the pics I promised, all for the bikes but it applies most to a 4 cylinder :snail:

http://ecomodder.com/forum/attachmen...0&d=1416438735

http://ecomodder.com/forum/attachmen...1&d=1416438735

http://ecomodder.com/forum/attachmen...2&d=1416438735

I would include a waterjacket on your header to speed up warmup. Not too much area or you'll have to upgrade your radiator, but it'll probably help economy more than anything else you can do.

Also, as was mentioned before, take a look at Mazda's design. They were advertising that a carefully designed header was crucial in letting them use extremely high compression.

I'd say you would need a "thermos bottle" coolant heat retention system in addition to that water jacket. It would have the reverse effect (cooling headers) until the coolant warmed up. Header Wrap would work all the time.

Well... I live in Australia, the temperature rarely hits less than 10 degrees C (50F) overnight (and almost never below 3-4C), and summer temps can get quite high, we've seen temps in the 45C (113F) range a few times in recent years. Plus I'm planning grille blocks, so improving exhaust insulation is likely to contribute to everything else under the hood being happier ;)

Plus, I feel that keeping the exhaust velocity high at low RPMs (through good insulation) probably trumps savings on the warmup cycle for a 30m drive, particularly with a modern engine - as I understand it, with newer engines the cylinders and valve train come up to temp in 30s to a minute, and modern oils (especially the thin stuff that Hondas apparently like) don't stay sticky very long. This is just gut feeling though - I should look at what improvements people with electric block heaters get. Of course even then, gains from an electric block heater would be larger than a water-jacket setup so it wouldn't be exactly equivalent.

Oh, I see. We are speaking of Engine Warmup, not header warmup :D

I would think that undersized cast iron "log" manifolds would benefit the most from cooler exhaust. Plenty of velocity already. The water jacketed manifolds would have their greatest benefit on a totally thermally managed ICE. There was a university that did an experimental "throttle-less engine" which basically used warmer air for lower RPMs, with less fuel to maintain the targeted AF ratios. Cooler Air Temps = Higher RPM and more fuel. Needless to say, FE (is that how they say Fuel Economy 'round here?) went up as well, due to greater thermal efficiency from the preheated air!

Everything I've read agrees "cold exhaust gas" = bad, especially at low RPMs. A few examples I've found of people implementing WAI (vs. stock intake) on Honda D-series engines also reported neutral or negative impact on FE, so I think it depends a lot on what the ECU is doing too.

If I did want hot air, I'd probably take it from a small jacket on or just after the cat. Plenty of waste heat to be had there.

Interesting about the 'throttle-less' engine - you could probably get a similar effect by running EGR at WOT... could be a good way to set up an efficient cruise control, for example, just open the throttle and use a big fat EGR valve to control power :p

I saw the X-pipe thing - both as a better alternative to an H-pipe for bank balancing on V-shaped engines, and the whole "Acoustic SuperCharger" / "The Amazing Campbell X-Pipe" thing... while I think it may have some merit in certain situations, I think it might complicate the design a bit in this case. One thing I was considering was having a an X at about 55-60" and then merging back to a Y at 80"-ish but I'm not convinced it would be worth it.

I'll say straight up that I think a lot of the wilder ASC claims on x-pipe.com can be attributed at least in part to the fact that the Campbell pipes don't have mufflers (and by the photos I could find, cats either - though they say "legal"... but elsewhere on the page they say "pleasure license only" so whatevs). Now the X-Pipe itself is a decent scavenging system, but with those advantages (removing muffler and possibly cat), you give any basically well-designed and built system a chance to really shine :D

There are some really interesting aspects to X-Pipes though. Consider that in a Y merge, you effectively double the excitation frequency in the pipe after the merge compared with before the merge (as you're adding two sets of pulses 180 degrees out of phase). This will affect any resonance that happens after that point. However, if an X-pipe (mainly) flows across the 'X' between opposite pipes, then each downstream tube will be effectively experiencing the same excitation frequency as the input, which would mean a wider resonance bandwidth (& less sensitivity to downstream pipe length) while still getting the scavenging effect. This could be very useful for high-revving engines, I would expect it to be especially handy on a motorbike.

And of course the flow isn't restricted by changing direction or going down a pipe size, so positive pressure pulse reflection should be lower compared to a basic (i.e. cheaply fabricated) Y merge. And of course the output tone will be much more meaty, as you avoid the frequency doubling effect mentioned... if I was building a big burbly V8 hot-rod, it would be a candidate for sure...

So plenty of interesting aspects, but not necessarily huge gains for a 'street' car with cats, mufflers and low RPMs (unless you believe all the hype ;) ) and quite a bit of added complexity.

If I had a good 1D simulation package I'd plug it in and see how it might go anyway, of course...

I'm amazed that no header manufacturer has not built or mass produced a tubing header for the VX. I'm not sure but think I read here that the CX uses the same manifold design. With the onset of cracking issues and the cost of factory replacements, close to $500, it would seem that there would be a market for a tubing header type aftermarket replacement.

The only rational reason for not producing one is that there just aren't that many of them (original CXs and VXs left to justify the start up costs, but even that makes little sense when all you need to do is get the intial setup for the computer to bend the components and weld them together.

Is there something I'm missing here?

regards
mech

Yikes... $500? Pretty sure I could put together a basic tubing header (exhaust ports to cat. flange) for the "cat in front of the motor" configuration in my shed for $400 and still turn a profit on the 'hand crafted' item... and that's including $150 for pre-made header flanges and sensor bungs. And in Australian dollars. Shipping could be an issue though, if most of the customers are in the US. As you say, the size of the market is probably the issue though - there's probably enough of them going through wreckers to soak up most of the market for them.

The reason you can't do this is because once the exhaust gas fraction is over 20% (less on some engines) it'll start to stumble. Plus, warm air is not as great as people here think, it increases the heat ratio and decreases thermodynamic efficiency. Running WOT with exhaust gas (even cooled) will probably induce knock.

Had a bit of a look at it (see autozine.org article)... basically the upshot seems to be that better scavenging allows higher compression ratios without knocking (very useful info! :thumbup:). As I'm planning a mini-me head swap soon with the option of a mild compression ratio increase, this is very good to know, this might persuade me to actually build a header ;)

The header geometry itself seems to be a standard 4-2-1 design, but the innovation seems to be that they've coiled the tube around the cat to warm it up faster, and also allow the longer length to fit in the engine bay given an exhaust-ports-at-the-back layout.

http://www.thetruthaboutcars.com/wp-...ld-550x365.jpg

Now I'm dubious about the "warms the cat up quicker" claim, it seems to me that the amount of radiation / convection heating at startup would be tiny compared to direct exhaust flow, but maybe that extra few percent gets them over some EPA-mandated "is your cat this fast to warm up" line :rolleyes:. In any case, I reckon just having a ceramic-coated SS manifold should be sufficient to do the same trick.

Well, I thought I might be able to get 80" before the cat... but I just did some measurements, and - bwahahahaNO. Based on not moving the cat, I have 18" from the cat flange to the centreline of the current bend, 15" from centreline of the exhaust up to the port centreline, 7" from port centreline to the top of the motor (which I'll call the max. vertical centreline for a ramshorn - there's room above but not much), 6" and change from the flange to the AC radiator, and 10" width to work with between the AC pump and where the gearbox bulges out - though I should be able to fit a pipe down the side pretty easily.

Straight pipes under the engine, with a bend up and then simple ramshorns give a max. pipe length to the cat. flange of about 18" (under the engine) + 15" (up to the level of the ports) + 4.5" (up to the start of the ramshorn) + 8" (180 degrees bend at 2.5" centreline radius) + 7" (90 degree bend at 4.5" radius) + 3" (start of the ramshorn to the port) = 55.5, give or take. About 26" short :D ah well, that's what drawing boards are for, huh?

Might be able to squeeze a bit more out with some clever routing, of course. Or I could just loop everything around like a tuba, would make trying variable geometry easier I guess ;)

Good news though, I measured the exhaust ports on a D head, they're 39mm x 28mm with a spacing of 84.5 (roughly - I wouldn't advise setting that running in a CNC mill ;) ). Which gives a port cross sectional area of 989mm, equivalent to a 1.4" pipe. So 1.375" primaries might work, with careful port matching on the header side. Also 1.625" OD tubing can be used for primaries and still leave room to jam an equal diameter pipe between them, which opens up possibilities.

Why do you not want a step in the "wrong direction"? I think it is only going to be a problem if you have long duration race cams...

A 32" primary is excessive and will miss out on some wave effects which could give extra scavenging between pipes, I think that should be the entire length of the header - a lot of people who write up and explain these equations, including professionals, don't understand them!

15 inch is about right depending on the speed of the exhaust flow down the pipes, going a few inches either way will just change the rpm at which you get best effect.

The most important decision is the pipe diameter, this controls the speed at which the exhaust gasses flow down the pipe, the thinner the pipe the faster they go and the faster they go the more inertia they have and the bigger the vacuum they can then pull behind them when the cylinder empties which in turn means more exhaust gas gets pulled out of the cylinder leaving less work for the piston to do in pushing out the remaining exhaust gas. If the piston does work to remove the exhaust gasses then that uses fuel, if the exhaust gasses do it then it is done for free. Essentially you want the pipes as thin as possible without them being so thin that they block the flow, the target speed is normally half the speed of sound, taking into account that the speed of sound is a lot faster at exhaust gas temperature, the reason people try to keep the exhaust gasses hot is to maintain a consistent speed of sound, although most people don't realise that. Once you get passed the half the speed of sound the exhaust gasses start having difficulty flowing and that gets worse as you approach the sound barrier.

If you want it to work well at low throttle then you need small diameter pipes to keep the gas flow speed up, the pipe lengths should then match those of a race header as the timings of flow and wave reflections will all be the same. You just need to make sure that the pipes are big enough for the flow to remain not excessive at full throttle and full rpm.

At least that is how I see it, others understand it in other ways...

Nigel, thats some good information! Its got to be tough to calculate the speed of sound in a medium that is shedding heat and becoming more dense as it travels through the tube. On my Beetle header I loose so much heat before it gets to my turbo its hard to get it to build its full boost potential. It takes tens of seconds under acceleration to build the header heat for the turbo to convert to the last 4 lbs of boost. I have Jetcoated headers but I'm going to wrap them and put aluminum around that to keep oil off of the wrap. So many variables to contend with. You have the amount of fuel being consumed adding changing temps in the exhaust flow and the temps already soaked into the header and the speed of the airflow around the header pulling heat out too.

If you are going to venture into header design, do yourself a favor and purchase Pipe Max ( PipeMax36xp2 ). I am unaffiliated, but it is highly regarded at Speed Talk forums, by guys that live and breathe this stuff. From dirt track to Nascar to 4000 hp pro drag cars, there's a lot of big engine builders on there that know there stuff, and trust the software.

Header design is a lot more than target an rpm and pick a diameter/length. Everything from camshaft timing & overlap, to EGT and engine displacement effect what the "best" exhaust is. Collector design is very important as well, be it a straight diameter/length, or getting into merge collectors with taper and volume coming largely into play.


And yes, you don't want to step down to a smaller area than the exhaust port. However, it's not completely unheard of to taper down to a smaller primary to keep velocities up, or form the tube end to fit inside the exhaust port to reduce cross sectional area. A step will cause an unwanted reflection wave back into the port, but a proper taper (<7 deg) will not cause issue. In most cases primaries are larger than the exhaust port, and a step in that direction will not cause so much turbulance, and will help break up the reflected wave from the end of the primary, which can fight low rpm reversion on engines with cam timing favoring higher revs.


The more I try and learn about header and intake design, the more I realize I know nothing. And getting it "right" the 1st time, without a dyno, is a pipe dream. Not saying you can't do something to make improve over stock, at least on older cars. But there's a reason GM will run hundreds of simulations before ever making a part, then test a few dozen different iterations.


Found this one interesting, primary "venturis". Supposably spread the torque curve out, and came in at a lower rpm, with no loss of top end power.
http://speedtalk.com/forum/download/...58d3d7f4ca814b

Well if you use the energy in the exhaust gasses to drive a turbo then the energy isn't available for extraction of the remaining exhaust gasses so the piston has to do the work instead using extra fuel. That's why a turbo engine of the same capacity as a NASP has lower fuel efficiency. It means that the design of the headers is not so important since all you are really interested in is driving the turbo sufficiently to give the boost while causing as little backpressure and thus extra work for the pistons as possible. Sounds like yours is a semi-turbo - trying to do both!

Many thanks Nigel, you've brought up a bunch of stuff I hadn't really considered, and spurred thoughts about a bunch more :thumbup:

I was under the impression that a step down in diameter would reflect part of the initial positive pressure pulse back into the cylinder, as well as restrict flow more than a step in the other direction?

I'd be right with you (as would the various formulae I've found) if I was designing for best scavenging at say 5800 rpm, but I'm looking for a torque boost closer to 2400rpm too :D. Though it looks like I may have to settle for less overall length (and torque boost at higher RPMd) due to space constraints.

Another nice thing about pulse resonance is that you get harmonics, so if there's resonance at frequency X from a long pipe (assuming closed pipe resonance, i.e. a restriction / reflector) you'll get a similar (albeit slightly weaker) effect at frequency 3X, so it's 'as if' you had a resonator 1/3 the length when you hit that frequency... not sure that will help of course

Do you know whether the 15" thing is about pressure pulses or flow? I haven't been able to find any explanation of this figure, apart from a couple of old quantitative parametric studies done ages ago on 351ci V8's, and those didn't attempt to answer the 'why' of it :confused:.

Not to mention that the speed of sound is also dependent on pressure, the size of the pipe (sound travels faster in a pipe than free air, and varies with diameter), and the fact that the speed of sound is measured relative to the medium, meaning sound travels faster going down the tailpipe than it does going back towards the engine :D. And of course pressure pulses travel at the speed of sound while mass flow is much slower, and positive pulses and negative pressure pulses react in different ways to steps in different directions, as does flow... Goodness knows I don't have my head around all of it yet...

Well, if say, you're running at half the rpm that the race header is tuned for, then the engine will be half as far along opening and closing valves etc. compared to where the race header is intended to deliver the reflections at... I can't see that being a good thing.

Another smaller effect I just realised, it even that to get the equivalent (single-tube) reflection times at part throttle I believe you need longer pipes - for a single pipe t(reflection) = t(going down the pipe) + t(coming back) = d / (v + v1) + d / (v - v1), where d is pipe length, v is the speed of sound and v1 is the speed of flow. If your full-throttle flow v1 is 1/2 the speed of sound v, then for a quarter the flow rate the pipes need to be about 30% longer for the pulse to return in the same amount of time - that's quite significant. Looking at the graph, I was thinking that maybe an even lower speed might be useful to keep part-throttle tuning consistent, if that's desired - 1/3 the speed of sound would keep the resonant frequencies within 10%, for example. Of course that would only apply to part-throttle at high RPMs. Interesting implication there too, in theory of your header is tuned for say 5500rpm and you're running at 6500 for example, backing off on the throttle might actually bring the header back 'into tune' by slowing down the exhaust flow... the relative effect is larger the higher the flow velocity, and would have more impact on a header with a narrow power band effect, could be a useful insight.

Cheers for that, I've been looking at finding some more comprehensive software. Could be handy to get closer to the ballpark than the formula approach, and it looks relatively affordable, I might just get it. Really what I'd like though is something which actually does FEA of the gas in the pipe, so I can 'touch' it and try unconventional things ;) - something like like WAVE (but it's about $500) or the GasDyn software developed by the Politecnica de Milano (but I don't think they even *sell* that one, I suspect you have to have a partnership with the university)...

Indeed - rpm and resonant frequencies isn't a bad place to start in figuring out a ballpark total size, of course ;) but yeah, there is indeed a lot more to it, as I'm discovering.

I asked because I didn't know. I suspect a pipe a little smaller than the port would be better for best economy, I would position it off centre so that the main flow didn't hit the step though, I haven't looked at your head but the main flow out of the port is unlikely to be down the centre of the port.

A step up in diameter creates a reverse wave which encourages flow which is why some manifolds have extra steps but the normal explanation for the header being wider than the port is to prevent exhaust going back into the cylinder during overlap on long duration cams which I don't understand but I guess has been found true by experiment. If you don't have long duration cams then there may be no issue.

Both are important but I believe flow is by far the most important. You need to work out how long the initial pulse of exhaust gas takes to travel down to the end of the primary at the exhaust flow speed, as it passes the other primary in its pair it will create a strong vacuum in that pipe via the venturi effect (same way airbrushes suck up the paint), the vacuum then takes time, dependent on the speed of sound, to act on the exhaust valve for that pipe and start to suck the exhaust gasses out of that cylinder, it continues sucking until the exhaust flow from the first cylinder slows, thus the time period of the exhaust flow needs to be taken into account to avoid wasting suction but sucking at the time it will have most effect. The same happens as the exhaust reaches the end of the secondary but there it sucks on both primaries of the other pair. The timings all get very complicated, then you have to add in the wave effects!

Most explanations are way off and conflict with each other, then I am sure some experts give the wrong explanation intentionally so that nobody else can work it all out!

I think the latest PipeMax does some simulation rather than just calculations as the earlier versions did. Don't know the details and most of these things are always used for full throttle on race cars so may need a lot of brainpower to come up with some results you can trust!

Haven't they used thermal imaging to see hot spots developed from the harmonics to choose where to put the crosspipes? That might help confirm if you're on to a good setup.

Maybe "trombone" exhaust header pipes, using sliding joints? At least for prototype testing?

Earlier postings:

• http://ecomodder.com/forum/showthrea...tml#post210603

• http://ecomodder.com/forum/showthrea...tml#post279467

• http://ecomodder.com/forum/showthrea...tml#post155270

• http://ecomodder.com/forum/showthrea...tml#post160892

• http://ecomodder.com/forum/showthrea...tml#post161499

I switched from a 4-2-1 catted equal length header to 4-2-1 unequal shorter headers and my mileage actually increased. This might be because i could run hella lot more timing at lower RPMs than before. Im talking about 6-10* of further timing advance. I'm not sure why, but i used to get much more bottom end knock with equal lengths.

Stock EL headers Catted:
Opening dimension: 1.378" ID
Primaries on the cat side are 25", 21" & 20" on driver side
1.772" ID collector
20" collector to first cat

New UEL Headers Catless
Opening dimension: 1.56" ID
Cross pipe length: 17"
Driver side collector length: 7"
Passenger collector to uppipe length: 13.5"
Header to uppipe opening: 1.75"

My cruising mileage was much improved at lower RPMs however at higher RPMs it seemed that for some reason my car liked to run richer. Even in closed loop the ratios were always a tad richer than target. about 0.2:1 AFR richer. this was nothing crazy but it did affect fuel economy. note the new headers have much higher flow rate and lack a catalyst converter.

Well, I've been thinking about layout and I have one setup in mind where it would be feasible change the secondary lengths by about 6" without too much trouble, just using clamps...

Thanks for the links, should make some good 'light' reading tonight ;)

That's exactly what I'd expect from the reading I've done, if the EL header was reasonably well tuned for high RPM - the reflected pulses would arrive at precisely the wrong time at lower RPMS, pushing gas back into the cylinder instead of sucking it out, which would explain both lack of torque and extra knock (as per the autozine article on the Mazda SkyActiv manifold linked earlier):

http://www.autozine.org/technical_sc...SkyActiv_1.jpg

Conversely if there's a bit of valve overlap and new header is scavenging less at high RPM, the ECU could be expecting a slightly larger larger air charge, and adding the right amount of fuel for the expected intake mass... though I'd expect closed loop control to correct that? It would depend on how closed 'closed loop' is, there may be saturation values in there which keep either internal or control parameters within predefined ranges - this is a common control systems 'hack' to stop a closed loop system from going unstable if some physical parameters change in an unexpected way :rolleyes:... depends on whether the person programming the ECS paid attention when they covered finding poles of a z-transform, and how much they expect the - and how much they trust the physical parameters of the system to not change. Of course, I'm no expert in ECS specifically, so I don't know whether that applies in this case.

When people talk about installing headers for performance, it's often mentioned that ECU tuning is required to get the best out of it... but I'm not sure if that's because they take it out of the closed loop parameter envelope, or

Yeah I consistently self tune my ECU . the header did not give me much trouble with exception of slightly richer AFR under load or high rpm. Most of this was fixed with MAF and o2 sensor rescaling. However under closed loop it is still too rich off the target and for some reason the ECU does not seem to compensate for it. I'm just not sure why. When I target 14.5 its actually at 14.3-14.4.

UEL Headers let me improve BOTH performance and economy by running richer with more timing until MBT is achieved. This was done using dyno. Under 2800 rpm which is pretty reasonable for city driving the engine does not go any richer than 14.0:1 (under heavy load) and timing is about 10* higher wthan before hich is very significant. Stock it was 14.5:1 with 10* retard. You might argue that richer AFR demolishes BSFC. Yes it does but the slight sacrifice in BSFC is made up for by shorter acceleration times and more power from extra timing. The acceleration with UEL headers is very linear and controllable. The drivebywire has been tuned to keep the throttle nearly wide open at low rpms and we have the TCU short shift. This way an inexperienced driver can accelerate nearly at best efficiency while keeping up with traffic yet never exceeding 2000 rpm. This I found was not possible with EL headers. The engine would shudder and sometimes detonate and it just was too slow. It just felt like lugging and now it feels smooth and 'torquey'. My peak torque also moved lower slightly from 4600 rpm to 4100 rpm and peak power was raised to 5800 from 5600. There is a secondary peak torque from this resonance yoy were mentioning at 2200 rpm but its not substantial like the one with EL headers (that was at 2800 rpm). Its a very flat curve now from 1800-5200 rpm vs 2800-5200 rpm as before with lots of dips and peaks. I'm surprised how much difference in the curve was made just by changing exhaust manifolds.

You know hotter headers flow better and shorter uel manifolds have a tendency to run hot.

If your header is creating more low end torque, wouldn't it make sense that it also creates more knock? Higher charge density = more knock, right?

Higher charge density at the same ignition timing should always mean better efficiency (assuming everything else is constant). However, if your engine must retard timing for a higher charge density, then you can obviously lower efficiency. It sounds like this is what is happening to you ever_green.

If the new header lessened reversion and therefor the amount of (hot) residual exhaust gases in the cylinder the more power could be made as well as reducing the chances of detonation.

That is because most engines don't run closed loop at full throttle, they use open loop and guess the amount of fuel to inject based on the throttle position sensor and either a manifold pressure sensor or air flow sensor.

A good manifold will create a higher vacuum in the cylinder which will pull the fuel/air mixture into the cylinder faster thus using more air/fuel mixture at any given throttle position so the throttle position sensor will be telling the ECU to put too little fuel in. A MAP sensor will show lower pressure in the manifold which the ECU will interpret as the throttle being closed more than it is thus requiring even less fuel. An air flow sensor should tell the correct story, but being slow to respond to changes the ECU will also look at the throttle position sensor which is telling the wrong story - You do need to change the mapping of the sensors for open loop running. Closed loop should be correct although any change in throttle position may cause temporary inaccuracy until the effect has been measured and corrected. Turning the fuel pressure up a touch should sort it unless the ECU has a fuel pressure sensor.

any non-detonating engine would make more power than a detonating one. plus sometimes its good to reduce VE a little to run more timing. hot rodders sometimes run less compression pistons to run more timing. there is a balance.

i did still get knock in closed loop at lower rpms...like 1600. this was addressed with slightly more closed loop fueling. it was not as horrid as stock where 10* of retard was needed.

Thanks Nigel_S, ever_green.

Unfortunately I don't have a lot of tuning options available to me - the ECUs supplied with Australian 6th gen Civics are either too primitive to update maps on, or just too small a market for tuning companies to make chips / add-on modules for. Whichever it is, as far as I can find out from internet forums and tuning kit manufacturer websites, the stock ECU is a black box as far as that's concerned. Now, one thing which I do have planned is a head swap using a D15Z7 head and ECU - same applies, it's an OBD2a ECU with no flashable memory, and I want to keep the stock ECU to correctly handle the 3-stage VTEC.

What I was planning there, given an ECU from a 1.5L engine on a 1.6L, was to carefully compare injector flow specs, and use an aftermarket adjustable fuel pressure regulator to increase the pressure 5-10% to keep the ECU within its parameters (especially in open loop mode) and keep the engine happy. On a side note, I went and spent money on parts before checking that theory :rolleyes: - am I on the right track there?

Do you think the same would work (i.e. with no ECU tuning per se) in terms of tuning open-loop fuel flow for a non-stock header (assuming the ECU can handle closed-loop conditions correctly in my case)? I presume doing this properly would require use of a dyno and appropriate exhaust gas measurement? It works in my head, just not sure how it will go in practice :p